1. Field of the Invention
The present invention relates to a process for preparing a thin film magnetic head having an excellent high density record property, more particularly, to a planarization process of an irregular surface caused by the existence of an electroconductive coil after forming a dielectric layer.
2. State of the Art Discussion
A conventional process for preparing coil type thin film magnetic heads and their construction is illustrated based on the drawings. FIG. 2 shows one embodiment of a coil type thin film magnetic heads prepared by a conventional method. A soft magnetic thin film, composed of Ni-Fe, Fe-Al-Si or Co-based amorphous alloys, is formed on a substrate 1 having good wear resistance, composed of alumina, ferrite, glass and the like, by means of sputtering, electron beam evaporation and the like and then etched to a desired shape by way of wet etching, ion beam etching and the like to form a lower magnetic core 2. On the lower magnetic core 2, an insulation layer 3 is formed, wherein electroconductive coil 4 is embedded in the insulation layer 3. The insulation layer 3 is made from SiO.sub.2, Si.sub.3 N.sub.4, Al.sub.2 O.sub.3 and the like by way of plasma-CVD, sputtering or electron bem evaporation. The electroconductive coil 4 is made from an electroconductive metal, such as Cu, Al and the like by way of electron beam vaporation, sputtering and the like. The electroconductive coils 4 are shaped to desired forms by wet etching or a ion beam etching. A general process for preparing the insulation layer 3 and the electroconductive coil 4 comprises forming the insulation layer 3, forming and etching the electroconductive coil 4, forming the remaining insulation layer 3, etching and forming a front magnetic gap layer and etching the insulation layer 3 to form a back core connection portion. Lastly, a soft magnetic layer 5, made from Ni-Fe, Fe-Al-Si, or Co-based amorphous alloy, is coated by sputtering, electron beam evaporation and the like and shaped by way of ion beam etching, wet etching and the like to form an upper magnetic core 5. In the process mentioned above, it is difficult that differences in level, caused by existence of the electroconductive coil 4, are sufficiently planarized. They induce irregular surface of the upper magnetic core 5.
However, in order to comply with the recent requirement for high density record, narrowing of truck and gap has been extensively studied in the field of thin film magnetic heads. This narrowing of truck and gap mainly requires accurate microproducing technique in the preparation process of the thin film magnetic heads. A dry process technique which has been presently used is capable of microfabrication to a considerable extent. Even in such dry processes, sufficient microfabrication is not obtained unless a lower portion of the thin film magnetic heads is sufficiently planarized. On the other hand, in the thin film magnetic heads, especially multitrack magnetic heads, plural layer construction is necessary for ensuring sufficient coil winding numbers for characteristics of magnetic heads. Accordingly, a desirable microfabrication by the conventional processes can not be accomplished unless planarization of differences in level caused by the electroconductive coil is sufficiently carried out.
Further, the irregular surface of the coil 4 has effects not only on the fabrication technique but also on magnetic properties of the upper magnetic core. In other words, the differences in level of the electroconductive coil causes irregular surface of the soft magnetic thin film (i.e. upper magnetic core), for which the magnetic properties of the soft magnetic thin film declines to cause problems, such as producing inferior permeability. These problems become very significant in a high frequency range.
As mentioned above, the planarization of the irregular surface is an important problem required from both fabrication technique and magnetic head properties. In order to comply with the requirement, there have been proposed a lift-off process and a planarization process by coating organic insulation materials such as a polyimide resist and the like. The lift-off process comprises forming an electroconductive coil layer, shaping to a desirable coil form with a photo-resist and then lamination of the insulation layer on the photo-resist which is left after shaping. However, this process has a problem in adhesion property, because the substrate can not be heated to a necessary temperature when the insulation layer is laminated. The organic insulation materials such as polyimide and the like also have problems in heat-resistance, and stabilities such as stability with time.